Noninvasive measurement of cauda equina dysfunction

Spinal nerve roots might be stimulated at the intervertebral foramen by percutaneous magnetic stimulation over the spine. We can record the compound muscle action potentials from the leg muscle elicited by paravertebral magnetic stimulation (PVM-CMAPs). Peripheral motor conduction time (PMCT) was determined by apprehension of the formula ((CMAP latency + F-wave latency -1)/2). The reaction time at the anterior horn cell was 1 ms. The difference between PMCT and the latency of PVM-CMAP showed cauda equina conduction time (CECT): CECT = PMCT - PVM-CMAP. We examined 16 healthy adults and seven patients with intermittent claudication due to lumbar spinal canal stenosis. CMAP and F-waves were recorded from the abductor hallucis (AH) with the tibial nerve electrical stimulation at the ankle. In 23 limbs of the healthy volunteers, CECT was 3.2 +/- 0.9 ms. In seven cases of lumbar spinal canal stenosis, CECT was prolonged (6.0 +/- 2.5 ms). There was significant statistical difference (p < 0.05) between CECT in healthy adults and CECT in lumbar spinal canal stenosis. It shows conduction slowing of the cauda equina exists in the lumbar canal stenosis. We can measure cauda equina dysfunction noninvasively by this method.